Process for recovering sugar values



Spt. 25, 1928.

R.'c. CAMPBELL PRocEss FOR REGOVERING swam mums 3 Sheets-Sheet 1 Filed May 1925 //V Vf/VTOI? was/Fr c. CHMPBELL Sept. 25,1928.

R. C. CAMPBELL PROUESS FOR RECOVERING SUGAR VALUES Filed Hay 7, 1m 3 sheets-shag; 2

INVENTOR.

Sept. 25,1928.

. 1,685,118 R. C. CAMPBELL PROCESS FOR nmcovsnlm SUGAR was K$WW EWRQRJU tefiwkanesw E INVENTOR. WEE/tram [AL incurring the expense Patented Sept. 25, 1928.

UNITED STATES 1,685,118 PATENT OFFICE.

ROBERT C. CAMIEBELL, OF MILLBURN, NEW JERSEY, ASSIGNOR TO UNITED FILTERS CORPORATION, OF HAZLETON, PENNSYLVANIA, A CORPORATION OF DELAWARE.

PROCESS FOR RECOVERING SUGAR VALUES.

Application filed May 7, 1925. Serial No. 28,549.

This invention relates particularly to improvements in the process and apparatus used in the recovery of sugar values from the muds separated from sugar juices. It may, however, be applied to other uses, as Wlll be understood.

It is an object of the invention to provide a process and apparatus whereby the amount of sugar recovered from the mud separated from the sugar juices particularly in the making of cane sugar maybe increased and at the same time the cost of handling these muds decreased from.the cost of handling according to the present procedure.

Another object of tllG'lIlVQIltlOIl is to provide a process and apparatus for sugar recovery which can be used in acontinuous operation in cane sugar and other mills w1th out stopping for the renewal or cleanmg of the filter cloths heretofore'used and without of renewing the .filter cloths as it has heretofore been incurred.

Another object of the invention is to provide a continuous process of sugar recovery wherein the mud from the sugar juices may be continuously filtered and the majority of the sugar recovered therefrom and the filter cake continuously fed to the furnaces w1th the bagasse, whereby the labor expense 1s reduced, the sugar recovery increased, and the expensive and unsanitary practice of dumping these filter cake muds 1n isolated places is eliminated.

Another object of the inventionis to provide a process and apparatus wherebythe sugar content of the sugar cane mud may be practically reduced to almost any deslred amount before the mud is removed from the filters and more efficient sugar recovery realized with a smaller amount of Water.

Various other objects and advantagesof the invention will appear as the description thereof proceeds.

Referring now to the drawings, whlch illustrate my process and one of the forms of apparatus suitable for carrying out the same,

Fig. 1 is a diagrammatic layout of a portion of a sugar recovering plant, in which my 1nvention is used;

Fig. 2 is a perspective view, and Figs. 3, l and 5 are detail sectional views of one form of filtering apparatus suitable for the purpose of my invention;

' as high as 3.5%.

use of additional equipment and the reintro-v Fig. 6 is a detail view of a filter leaf sector provided with the filtering medium; and

Fig. 7 is a diagrammatic illustration or flow sheet of the cane and sugar juices through the mill according to my improved process.

In the recovery of sugar juices particularly fromsugar cane as heretofore practiced, it has been the custom to defecate the juices from the crushers and the first mills with lime or other chemicals, heat, and run into intermittent or continuous settling tanks or thickeners of any desired type, and permit the sediment or mud, as it is called, to settle out or be separated from the juices, while the clarified juice is drawn off from the top andsent to the evaporators, the mud being withdrawn from the bottom of the settling chamber or clarifier, diluted with water to reduce the sugar values therein, filtered, and discarded. The discarded mud after being filtered, is ordinarily dumped into a suitable railway car and hauled some distance firggi the plant where it is spread upon the According to another process of sugar recovery, the mud from the first settling tank is introduced into a secondary settling tank to gether with certain of the juices from the later mills and again permitted to settle or clarify, the mud from this second tank being mixed with later juices and deposited on-th'e cane or bagasse passing through the mills and burned with the bagasse in the furnaces.

In each of these processes the sugar loss is comparatively high. In the filtration process using the ordinary plate and frame filter, the discarded mud may contain as much as 5% of sugar, the filtering operation is intermittent, the cost of operating the filters,

In the second process the sugar loss may run This process requires the duction of the first mud into the second and third juices increases the time that this mud is kept in process and the consequent danger of fermentation and inversion.

According to my invention, it is possible to continuously filter the muds from the first settling tanks of a sugar cane mill without redefecation so as to produce a clear filtrate therefrom and to reduce the sugar content to any desired limit, easily to less than 1%, and

haul- 1 ing away the cake, etc., and the cost of filter cloth, makes this a very expenslve process.

at the same time produce a partially dried mud or filter cake which may be conveniently conveyed around and added to the bagasse near the last mill and burned with the bagasse in the furnaces without returning it to the juice in process. The use of filter cloth and the expense thereof is eliminated and less labor is required than in the older processes.

It will be understood that the preferred form of apparatus selected for the illustration of the process is used solely for the purpose of illustration and is not to be considered as limiting the invention to the particular filters used or to the particular type of 'clarifiers illustrated, or to other details of the process or apparatus.

In Fig. 1 I have indicated a clarifier or settling tank 1 for the first uices of a sugar cane mill which preferably should be of the continuous type and may be of the Dorr or any other desired form. The clear juices from this tank overflow near the top of each compartment, are removed from the apparatus and conducted to the evaporators,and the mud and-settlings, growing continuously thicker as they near the bottom, are withdrawn through the pipe 2 into a suitable tank 3 containing the sludge or material to be filtered. The tank 3 is preferably provided with a stirrer or agitator 4 and in order to produce a mud of the consistency for proper filtration, the mud may be diluted by means of water from the pipe 5 or from a portion of the filtrate, as will be described later, if the mud from the clarifier is too thick. I have found that a thick mud produces a thick cake on the surfaces of the filter the outer portion of which is so soft that it runs back into the tank when the filtering surface is removed therefrom, and in order to produce a firm cake I dilutethe mud so as to get a larger volume of filtrate and a higher rate of filtration which gives me a thinner but firmer cake. Itwill be understood that where mud of the proper consistency to form the desired cake is formed in the clarifier or settling tank 1, the mixing tank 3 may be omitted and the mud conveyed or pumped directly to the filter 6. From the mixing tank 3 the sludge or mud is pumped through the pipe 7 to a filter 6 which may be of any preferred type provided with my improved filtering medium and adapted to operate continuously according to the improved process which will hereinafter be described. In the specific embodiment illustrated, the filter 6 is of the continuous suction type and comprises a tank or tanks 7 for the filtrate, a rotating central shaft 8 carrying a plurality of filter leaves 9 adapted to rotate and dip into the tank 7 Suction is communicated to each ofthe filter leaves through the central shaft 8 by means of a vacuum pump 10, so that durin the rotation of the leaves 9 through the tan lxs 7 the fluid is drawn'through the filter surfaces of the leaves and through the central shaft 8 and discharged into the tanks adapted to receive the filtrate, and a cake of the mud or material being filtered is deposited on the leaf, and during a portion of the rotation of the leaves outside the tank 6, wash water may be sprayed on the filter cake from the pipes 21 and sucked through the filter to wash out the sugar or other values from the cake. This type of filter is not claimed as a part of the present invention, as it is well known in the general art under the name American continuous filter, and is shown and described more in detail in the patent to Orange J. Salisbury, N 0. 1,259,139, granted March 12, 1918.

According to my invention the filtering medium applied to the leaves of this filter comprises on each sector of the leaf a smooth,

, hard but permeable material which may be in the form of a fine screen which has been heavily rolled to produce smooth surfaces thereon or a perforated or slit metallic plate 9? having perforations, slits, or the like of about .020 inch in diameter or width, and having as much of the area as practicable covered with these perforations or slits, there being preferably about six hundred or more perforations per square inch of the plate material, the exposed surface of the plate being smooth. These plates or smooth screens are secured to the surface-of'the filter leaves by screws or the like. These perforations cannot ordinarily be made small enough to prevent a portion.of the mud or cake from escaping therethrough, so that the first filtrate flowing through the leaf is not entirely clear. After a short time, however, a filter cake of sufiicient thickness and imperviousness is built up on the surface of the leaf to form an efficient filtering layer which produces a clear filtrate. I, therefore, during the first few seconds of the filtration, run the muddy or cloudy filtrate into a receiver 11 from which it is pumped back to the mixing tank 3, Where it dilutes the mud from the clarifier, or to the clarifier 1, if a mixing tank is not used, and during the remaining portion of the rotation ofthe leaf, draw the clear filtrate and the wash water containing the sugar values into a receiver 12 from which it may be pumped to the evaporators for the recovery of the sugar therein. It will be understood, of course, that the clear filtrate and the wash water may be separated-and the filtrate containing a high sugar value sent to the evaporators while the wash water containing, a lower sugar value may be returned to the process.

As the filter leaves 9 enter the sludge or mud in the tanks 7, the suction from the pump 10, communicated to the receivers 11 and 12, draws the filtrate through the perforated plates 9 on the leaves 9 and through the filtrate channels 13, located around the central shaft 8 to the valve 14 which automatically controls the discharge thereof.

I with the small compartment of the valve chamber which receivesv the first or muddy filtrate while the pipe 1:2 communicates with the larger compartment 15 which receives both the clear filtrate andthe wash water.

Compressed air or steam may be admitted through the compartment 15 to blow in a. reverse direction through the filter leaves as they are passing the scrapers 16 at the entrance to the tanks 7 to assist in loosening the cake. An outlet 15 for the excess air or steam permits its escape as the leaves are immersed in the sludge. The scrapers 16, which may be of rubber or the like, are located at the entrance to the tanks and press against each side of the filter leaves and scrape the cake cleanly therefrom, leaving substantially no residue on the plates 9, the cake falling gown between the tanks 7, as indicated in The relative duration of the two filtration periods and the washing period may be varied as desired. I have found, however, the following proportioning to work out very well in practice. The compartment 15 is of such a size as to permit a muddy or cloudy filtration period of from five to fifteen seconds, at which time a preliminary cake has been built upon the surface of the leaves 9, sutlicient to stop all further flow of cake through the filter leaves and to make a completely clear filtrate. The clear filtration period is preferably of forty-five to fifty-five seconds duration, followed by a washing period of about three minutes, which has been found sufficient to reduce the sugar values in the cake below 1%. The entire rotation of the leaf takes approximately nine minutes, and at each rotation the cake is formed on the leaf and completely discharged. The discharged cake containing less than 1% of sugar values, is scraped from the sides of the leaf by the scrapers 16 and is preferably dropped upon a continuous conveyor indicated by the dotted line 20, and carried to a point near the last cane mills, where it is dropped on the bagasse before the bagasse passes through the last rolls of the mill. Here it is compacted, so that the filter cake and bagasse may be burned together in the fur uaces. If desired, the filter cake may be diluted in the tank 6 and pumped as a thin sludge to the bagasse.

The operation of the filter is automatic. No disassembling and assembling is necessary as in the plate and frame type filters heretofore used, and the perforated plate filtering medium presents a smooth surface to the scrapers or cleaning devices 16 and last indefinitely, wear on the surfaces of the plate by the scraping action is infinitesimal, and

due to the smoothness of the surface of the plate and the fact that there is no rough layer as in the woven wire or textile filter cloth, complete cleaning at each rotation of the filter leaf is realized. There is no necessity for special defecation or other special treatment of the juices or muds to facilitate filtration as the filter is capable of handling any muds which the plate and frame filters now handle. Where a smooth filtering material can be used which is sufiiciently dense to produce a clear filtrate from the start, the preliminary or cloudy filtration period may be dispensed with.

legends applied thereto in view of the pre-' ceding description are self-explanatory. In this drawing the solid lines indicate the normal flow of materials according to my new process and the dotted lines show some (but not all) of the changes from the preferred flow which may be resorted to. The dotted line a indicates that the mud may go direct from the clarifiers to the filter and the line b that the muddy filtrate may be returned to the clarifier. The line 0 indicates that the clear filtrate may be returned through the clarifier to theevaporators and the dotted lines d and tank 6 indicate that the filter cake may be mixed with water before being placed on the bagasse or may be mixed with water and refiltered to still iurther reduce the sugar content.

While I have described the perforated metallic plate as the preferred filtering medium,

it will be understood that other smooth, hard and permeable filtering materials may be used, such as porous, smooth stone, smooth, perforated ceramic materials, hard rubber, or other hard, smooth, porous or perforated materials suitable for the purpose, and that the exact number or size or shape of the perforations is not material to the invention. The filtering material is preferably as noncorrodible as possible toward the fluid being filtered.

It will also be understood that various other types of filtering apparatus equipped with a perforated plate filtering medium could be used, such as, for. instance, the drum filter, or any other continuous filter, and that the layout need not be exactly as depicted herein, in order to achieve the results and advantages of my process. The invention is therefore not limited to the details of the process or apparatus, but is intended to include anything coming within the spirit of the invention and the scope of the appended claims.

I claim:

1. The method of recovering sugar values from the muds separated from sugar juices which comprises continuously filtering the .muds, continuously returning the cloudy portion of the filtrate to a previous point in the process, continuously collecting any remainmg portion of the filtrate and continuously washing the filter cake and collecting the wash water, and completely cleaning the filter each cycle of operation.

3. The method of recovering sugar values from the muds separated from sugar cane juices by the use of a continuous filter provided with a smooth perforated filtering medium which comprises continuously filtering these muds, continuously returning the first filtrate to the supply of unfiltered mate rial until a filter cake has been formed on the surface of the. filter sufficient to produce a clear filtrate, gathering the clear filtrate and wash water, and completely cleaning the surface of the filtering medium at each cycle of.

filter operation.

4. The method of recovering sugar values from the muds separated from sugar cane juices by the use of a continuous filter which comprises defecating and heating the juices, separating the clear liquids from the mud in clarifiers, diluting the separated mud to form a hard filter cake continuously filtering the mud without further defecation, washing the muds on the filter surface to reduce the sugar content thereinand completely removing the filter cake from the filter surface during each filter cycle.

5. The continuous method of recovering sugar values from the muds separated from sugar cane juices which comprises defecating and heating the juices, separating the clear liquids from the mud, separating the cloudy and clear filtrate in continuous separators, diluting the separated mud and continuously filtering the mud, washing the filter cake on the filter surface, and completely removing the filter-eake from said surface during each filter cycle.

6. The continuous method of recovering sugar values from the muds separated fro-m sugar juices which comprises defecating and heating the juices, separating the clear liquids from the mud in continuous separators, diluting the separated mud and continuously filterdefecating the juice obtained by crushing,

heating, settling and passing the so clarified j nice to the evaporator-s continuously filtering the mud from the settling, continuously col-' lecting the first ortion of the filtrate until the filtrate runs 0 car, continuously returning said first portion of the filtrate to the supply of unfiltered mud, collecting the clear portion of the filtrate, continuously washing the filter cake on the filter surface and continuously and completely removing the filter cake from' the filter surface during each rotation of the filter and depositing on the bagasse as it passes through the mill, whereby it may be burned with the bagasse in the furnaces.

9. The process of extracting sugar from canejuices which comprises crushing the cane, defecating the juice obtained by crushing, heating, settling and passing the so clarified juice to the evaporators, continuously filtering the mud from the settling, continuously collecting the first po-rtion of the filtrate until the filtrate runs clear and continuously returning said first portion of the filtrate to the supply of unfiltered mud, collecting the clear portion of the filtrate, continuously washing the filter cake on the filter surface, completely removing the filter cake from the filter surface during each rotation of the filter, mixing the filter cake with water or dilute juice to reduce the sugar content thereof, and refiltering.

10. The method of filtering a sludge which normally clogs the pores of the woven filter fabric, which comprises supplying the sludge to a continuous filter, having a hard, smooth porous'filtering surface, forming a filter cake on the surface of said filter, continuously returning the cloudy filtrate collected during the formation of said filter cake to the supply I of unfiltered material, collecting the clear filtrate produced after the formation of said filter cake, and completely cleaning said filtering surface during each cycle of operation.

11. The method of filtering muds from sugar cane juices and the like, which comprises supplying the muds to a continuous filter having a hard, smooth perforated filtering surface, forming a filter cake'on the surface of said filter. continuously returning the cloudy filtrate collected during the formation of a preliminary filter cake to the supply of unfiltered material, collecting the clear filtrate produced after the formation of said preliminary cake, washing the filter cake on said filter surface, substantially completely cleanin said filtering surface during each cycle 0 operation.

12. In the recovery of sugar values from the muds separated from the sugar juices, the step which comprises continuously filtering the muds from the clarifiers, continuously returning the filtrate to an earlier step in the process, continuously washing the filter cake on the filter surface and continuously removing all of the cake from the filter surface during each cycle of filter operation.

13. The step in the process of sugar recovery from sugar cane juices which comprises continuously filtering the muds from the settling tanks without. furtheridefecation, continuously washing the cake on the filter to reduce the sugar contentand completely removing the cake during each cycle of filter operation.

14. In the process of extracting sugar valuesfrom sugar cane muds by the use of a continuous filter, the step of continuously returning the first cloudy filtrate to a previous stage of the process, passing the later clear filtrate to evaporators, washing the filter cake, and completely cleaning the filter surface during each cycle of filter operation.

In testimony whereof I have afiixed my signature to this specification.

ROBERT C. CAMPBELL. 

